1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus such as a copier, a facsimile, and an image forming apparatus, and more particularly, to an image forming apparatus that includes a process unit that utilizes a charger for charging either a surface of a latent image carrier, toner on the surface of the latent image carrier, or both.
2. Discussion of the Background
Generally, an image forming apparatus employing electrophotography forms an image in the following manner: A latent image carrier such as a photoreceptor is evenly charged and exposed so as to form an electrostatic latent image. A developing unit develops the electrostatic latent image to produce a toner image. Subsequently, the toner image formed during development is transferred to a recording medium such as a transfer sheet or the like from the latent image carrier, or the toner image is transferred to the recording medium through an intermediate transfer member.
Such an image forming apparatus uses a charger that applies a charging bias to a charging member such as a charging roller or the like, which is conductive and abuts a surface of the latent image carrier. Accordingly, discharge is generated between the latent image carrier and the charging member, thereby evenly charging the surface of the latent image carrier.
Furthermore, a charger that performs secondary charging is also known. For example, according to JP-2005-62737-A, such a charger includes a charging roller and a scorotron charger serving as a main charger that evenly charges the latent image carrier as well as a secondary charging member to which a secondary charging bias is applied. The secondary charging member comes into contact with a place on a continuous moving surface of the latent image carrier that has passed through a transfer process before being charged by the main charger. Discharge or charge injection from the secondary charging member secondarily charges the surface of the latent image carrier before the main charger evenly charges the latent image carrier. Furthermore, residual toner adhering to the surface after transfer (transfer residual toner) is charged to a normal charge polarity.
As a result of all the above-described operations, uneven charging of the latent image carrier can be suppressed. In addition, contamination of the developing region due to weakly charged toner and/or oppositely charged toner being re-transported to the charging region can be reduced, if not prevented entirely. Moreover, contamination of the charging member due to the weakly charged toner and/or the oppositely charged toner being transferred to the charging member can also be prevented.
However, when the transfer residual toner firmly adheres to the conductive member serving as the charging member abutting the latent image carrier and to the secondary charging member, such a charger has a drawback in that the transfer residual toner and/or the latent image carrier surface intervenes between the discharge and/or the charge injection between the charging member and the secondary charging member. Consequently, the main charging and/or the secondary charging may not be performed well, thereby causing uneven charging. Furthermore, the transfer residual toner may not be appropriately charged, causing contamination of the surface of the latent image carrier. Contamination herein refers to a phenomenon in which the toner adheres to the surface (the evenly charged portion) of the latent image carrier.